Over the past few years widespread use has been gained in opthalmosurgery by surgical instruments for carrying out intraocular surgery through a small (under 1.5 mm) incision in the ocular wall.
One state-of-the-art ophthalmological instrument is known, which is in fact a cutting instrument executing reciprocation motion and having a channel for the vitreous humor to aspirate. The cutting knife of the instrument shaped as a hollow tube receives reciprocating motion from an electric motor accommodated in the instrument grip. The knife is coaxially mounted in the outer tube having one closed end to form a working endpiece together therewith, an opening being provided in the side wall of the outer tube close to its end (U.S. Pat. No. 4,108,182).
The intraocular tissue to be removed is sucked into the interior space of the outer tube by virtue of a negative pressure built up in the hollow inner tube and imparted through its open end to the opening in the outer tube. When extended the knife pointed end, while closing the opening in the outer tube, cuts off the tissue located inside the tube, whereupon the cut-off tissue is removed from the eye by aspiration. Then the knife returns into the initial position, thus exposing the opening in the outer tube, and the whole operating cycle is repeated.
However, the fact that the drive is accommodated in the instrument handgrip adds to its weight and causes parasitic vibrations of the working endpiece. Besides, provision of an electric motor in the instrument makes its sterilization difficult. The instrument construction makes no provision for adjusting the working stroke and the force applied to biological tissues.
One prior-art ophthalmological instrument features its working endpiece made up of two tubes in a manner described above, while a drive which is in fact an electromagnet, is brought outside the handgrip and is associated with the endpiece through a flexible tie-rod enclosed in a sheath (SU, A, 980,710). However, the aforesaid instrument is very sensitive to flexures of the flexible tie-rod which are inevitable in the course of surgery. Such sensitivity is causative of higly undesirable variations of the working endpiece stroke amplitude. In addition, bad vibrations are imparted to the working endpiece due to elctromagnet kicks.
One more ophthalmological device known in the present state of the art is adopted as the prototype; it comprises a cutting instrument in the form of a working endpiece which incorporates a stationary fixed outer tube having a closed free end and a side hole nearby said end, and an inner tube, which is in fact a movable element of the cutting instrument, having a pointed free end and being capable of reciprocating motion. The working endpiece may be made as microscissors. The device comprises also a handgrip on which is fixed the working endpiece and which accommodates a part of the drive made as a bellows mechanically associated with the movable element and connected to the flexible tube.
The drive is in fact a pneumatic system consisting of a compressor, control members of said compressor, and a flexible tube whose one end communicates with the compressor and the other end, with the bellows accommodated in the handgrip (U.S. Pat. No. 3,884,238).
Since the endpiece is introduced directly into the operative field the output power of the pneumatic drive is limited, whereby the drive fails to provide an adequate force applied to the movable element which is required, in particular, for cutting through dense intraocular tissues, e.g., the pupillary membranes, fibrous vitreous adhesions, and some other similar tissues. Besides, such a drive is unadaptable to adequately reliable forceps for gripping foreign bodies or membranous cataracts. Attempts aimed at increasing the drive power by elevating air pressure in the pneumatic drive are fraught with a danger of air inrush into the operative field. Moreover, the operating chain `control pedal - electric control circuit - compressor - valving system - power fluid (air being known as highly compressible working fluid) - bellows - working end-piece movable element` features but inadequately quick action. This in turn results in that surgeon's decisions are executed with some delay in the course of surgery.
The surgeon is rather inflexibly bound to the mode of the device operation, since the operating modes are changed on the control panel, which involves the presence of a technically skilful operator in the operating room.
The scope of the disadvantages mentioned above results in that the surgeon has but an inadequate direct control over the operation of the device, i.e., he has to rely upon such factors as reliability and operating capabilities of a complicated electromechanical arrangement, promptness and adequate comprehension of auxiliary attending personnel stable operation of power mains, and some other, which are far from ensuring exact and instantaneous execution of surgeon's decisions. In its turn an inadequate direct surgeon's control over the operation of the instrument leads to affected safety of intraocular surgery and lower efficacy thereof in cases where surgeon's decisions fail to be executed in a full scope due to its going beyond the limits of the instrument capabilities.